In a backlight unit of a large-sized liquid crystal display apparatus, a plurality of cold-cathode tubes is arranged immediately below a liquid crystal panel. These cold-cathode tubes are used together with members such as a reflecting plate that reflects emitted light from the cold-cathode tubes to a side of the liquid crystal panel and a diffuser plate for diffusing light emitted from the cold-cathode tubes to thereby make a surface light source.
In recent years, a light-emitting diode has been used as a light source of this type of backlight unit. The light-emitting diode has been improved recently in its efficiency and is expected as a light source that consumes less power and replaces a fluorescent lamp. Additionally, when the light-emitting diode is used as a light source of the liquid crystal display apparatus, it is possible to reduce the power consumption of the liquid crystal display apparatus by controlling the brightness of the light-emitting diode according to video images.
Incidentally, as a light-emitting diode for a liquid crystal display apparatus, a type in which a blue light-emitting diode using a GaN semiconductor as an active layer is combined with a phosphor is becoming mainstream.
FIG. 15 is a diagram illustrating a structure of a GaN light-emitting diode disclosed in PTL 1. As illustrated in FIG. 15, in the light-emitting diode, n-type contact layer 32 formed of an n-type GaN film and n-type clad layer 33 are formed on sapphire substrate 31 via a buffer layer (not illustrated). Light-emitting layer 34 formed of an InGaN film is formed on n-type clad layer 33, and p-type clad layer 35 formed of a p-type AlGaN film and p-type contact layer 36 formed of a p-type GaN film are formed on light-emitting layer 34 sequentially from a bottom thereof. N-type electrode 37 is formed on n-type contact layer 32, and p-type electrode 38 is formed on p-type contact layer 36. Light-emitting layer 34 emits light by applying a voltage between n-type electrode 37 and p-type electrode 38.
According to the light-emitting diode disclosed in PTL 1, a largest amount of light is emitted in a front direction of a chip of the light-emitting diode. Therefore, light emitted from the chip in the front direction is diffused by refraction using a lens, through a concave face near an optical axis, so that luminance on an illuminated surface near the optical axis is subdued, and an illumination distribution is made wider.
It is an object of the present invention to provide a light-emitting diode having a light-emitting characteristic with wider distribution of light, a backlight unit that is inexpensive and has a high efficiency using this light-emitting diode, and a liquid crystal display apparatus having an improved image quality using this backlight unit.